All-in-one computer system peripheral devices are becoming common place in modern day computer systems. Such combination peripheral devices, such as a combination scanner-copier-printer, are convenient and facilitate home-office networking allowing professionals to provide company services from their homes rather than in the environment of a high overhead office.
Combination devices have become available in the marketplace because of the lower manufacturing costs associated with storing digital information. In this regard, a scanner is able to scan a document and convert light reflecting from the document into an analog electrical signal in a fast and efficient manner at a relative low cost. Analog to digital converter facilitate converting such an analog signal into a digital signal that permits the document to be displayed on a computer video monitor, immediately printed as a duplicate document, or if necessary stored temporarily for multiple copy purposes.
The conventional scanner in such an all-in-one peripheral device typically include a traveling light source for illuminating indicia and background surfaces of a document to be scanned, a charge coupled device, otherwise known as a CCD, for converting the light reflecting from the surface of the document into an electrical signal, and a light transmissive member for supporting from below, in a stationary manner, the document to be scanned. The resulting electrical signal is then processed to digitize the information content of the scanned document so that it may be displayed on a computer video monitor and if required subsequently stored for multiple copy purposes or later retrieval.
While such scanners are quiet, fast, and highly reliable, those skilled in the art are aware that various compensation circuits must be employed to control amongst other things, variations in illumination levels produced by the traveling light source due to lamp warm up and light dispersion problems, such as light piping.
Such compensation circuits typically include a lamp feedback system that controls the electrical signal output level of the CCD to compensate for the above-mentioned variation factors. In order to provide the feedback system with a positive, reliable indication of the intensity of the lamp as it is traveling relative to a document supported on the light transmissive member, a light reflective member or white colored strip is mechanically affixed to the surface of the light transmissive member for reflecting light back to the feedback system.
While the light reflective member provides a positive indication of the intensity of the lamp during its warm up period, the reflective member has not proven to be entirely satisfactory relative to providing a reliable indication of the intensity of the lamp in a cost effective manner. In this regard, the reflective member must be maintained in close intimate contact with the transmissive member to provide a reliable feedback of the intensity of the lamp throughout the entire path of travel followed by the traveling light source. Moreover, the reflective member must be painted on the transmissive surface in a tightly controlled manner, avoiding bubbles, pits, fibers and other contaminates, to provide a smooth reflective surface with uniform light reflective properties throughout the entire length of the strip. Providing such a tightly controlled strip, is not only time consuming, but is also relatively expensive.
Other problems are also associated with a painted strip. For example, because of the large tolerance stack or distance between the light receiving member and the light converting CCD member, there is a substantial lost in CCD pixel image conversion area that would otherwise be available. Moreover, as such a strip is opaque throughout its length, light piping occurs resulting in unwanted and undesired light dispersion. Thus, to compensate for the effect of such dispersion, complex and costly approximation firmware is required.
Therefore, it would be highly desirable to have a new and improve lamp feedback system that provides a positive control signal that is indicative of variations in lamp intensity along a predetermined path in a highly reliable and relatively inexpensive manner. Such a new and improved feedback system should not require the utilization of complex and costly approximation firmware to compensate for the effects of light piping, nor the manufacturing of an expensive transmissive member with an elongated opaque paint strip having uniform thickness throughout its entire length.